The present invention relates to an emission controller for an electronic flash associated with an electronic camera which includes a solid state pickup element (solid state image sensor), and more particularly, to such emission controller which enables an image to be obtained which is synchronized with the emission of flashlight from an electronic flash.
When using an electronic flash including a solid state pickup element, it has been difficult to take a picture of an instantaneously moving object in synchronism with such movement while utilizing an electronic flash. By way of example, when a scanning takes place according to an NTSC (National Television System Committee) scheme to read intermediate picture elements from the solid state element, and an electronic flash is triggered to emit flashlight, it will be seen that the resulting picture will be distorted in terms of the amount of light incident thereon since the duration of the emission from the electronic flash is on the order of several milliseconds at most. In other words, if the emission of flashlight is initiated from the electronic flash independently of a vertical sync signal, a video signal will contain pseudo-signals, which causes bright lines to appear across the image.
To compensate for this, there has been proposed an emission controller for an electronic flash for use with an electronic camera in which the electronic flash is triggered in synchronism with a vertical sync signal so that the emission of flashlight takes place within a vertical blanking period. Specifically, the controller operates to initiate the emission of flashlight from the electronic flash in response to a logical product of a flash trigger signal and a vertical sync signal. However, it will be seen that with such conventional arrangement, the emission of flashlight from the electronic flash may occur with a time delay up to a maximum of the period of one frame, which is about 30 milliseconds in the NTSC system, after a trigger switch associated with the electronic flash has been closed, since the emission is not initiated if the trigger switch is closed until the vertical sync signal occurs. As a result of this time delay, the chance to take a picture of an object being photographed which moves instantaneously may be missed.